Field of the Invention
The present inventions relate to polyorganic compositions, methods, structures and materials; polymer derived preceramic and ceramic materials and methods; and in particular polysilocarb compositions, methods, structures and materials. The present inventions further relate to methods for making Silicon Carbide (SiC) and SiC compositions, structures, components, materials and apparatus for making these items; methods for making Silicon Carbide (SiC) and SiOC compositions, structures, components, materials and apparatus for making these items; and in particular, to SiC that is made from polysilocarb materials. Polysilocarb materials and methods of making those materials are disclosed and taught in U.S. patent application Ser. Nos. 14/212,896, 14/324,056, 14/268,150 and 14/634,819, the entire disclosures of each of which are incorporated herein by reference.
Materials made of, or derived from, carbosilane or polycarbosilane (Si—C), silane or polysilane (Si—Si), silazane or polysilazane (Si—N—Si), silicon carbide (SiC), carbosilazane or polycarbosilazane (Si—N—Si—C—Si), siloxane or polysiloxanes (Si—O) are known. These general types of materials have great, but unrealized promise; and have failed to find large-scale applications or market acceptance. Instead, their use has been relegated to very narrow, limited, low volume, high priced and highly specific applications, such as a ceramic component in a rocket nozzle, or a patch for the space shuttle. Thus, they have failed to obtain wide spread use as ceramics, and it is believed they have obtained even less acceptance and use for other applications.
To a greater or lesser extent all of these materials and the process used to make them suffer from one or more failings, including for example: they are exceptionally expensive and difficult to make, having costs in the thousands and tens-of-thousands of dollars per pound; they require high and very high purity starting materials; the process in general fails to produce materials having high purity; the process requires hazardous organic solvents such as toluene, tetrahydrofuran (THF), and hexane; the materials are incapable of making non-reinforced structures having any usable strength; the process produces undesirable and hazardous byproducts, such as hydrochloric acid and sludge, which may contain magnesium; the process requires multiple solvent and reagent based reaction steps coupled with curing and pyrolizing steps; the materials are incapable of forming a useful prepreg; and their overall physical properties are mixed, e.g., good temperature properties but highly brittle.
As a result, although believed to have great promise, these types of materials have failed to find large-scale applications or market acceptance and have remained essentially scientific curiosities.
Silicon carbide (SiC), is a compound of silicon (Si) and carbon (C) that has wide ranging uses, applications and potential for future uses. Eugene Acheson is generally credited with developing the first commercial processes for making silicon carbide, which are taught and disclosed in U.S. Pat. Nos. 492,767 and 560,291, the entire disclosures of each of which are incorporated herein by reference. Silicon carbide is a highly versatile material. Silicon carbide can have several forms, e.g., amorphous, crystalline having many different polytypes, and forming single (or mono-) and polycrystalline structures. Silicon carbide finds applications in among other things, abrasives, friction members, and electronics. Silicon carbide powder, fines, pellets, or other smaller sized and shaped forms, can be joined together by way of a sintering operation to form component parts and structures.
Generally, silicon carbide can function as a semiconductor. As a material it very stable. Silicon carbide is a very hard material. It is essentially chemically inert, and will not react with any materials at room temperature.
In recent years the demand for high purity silicon carbide, and in particular high purity single crystalline carbide materials for use in end products, such as a semiconductor, has been increasing, but is believe to be unmet. For example, “single crystals are gaining more and more importance as substrate[s] for high frequency and high power silicon carbide electronic devices.” Wang, et. al, Synthesis of High Power Sic Powder for High-resistivity SiC Single crystals Growth, p. 118 (J. Mater. Sic. Technol. Vol. 23, No 1, 2007)(hereinafter Wang). To obtain these high purity silicon carbide end products, silicon carbide powder as a starting or raw material must be exceedingly pure. However, “[c]ommercially available SiC powder is usually synthesized by carbothermal reduction of silica. Unfortunately, it is typically contaminated to the level that makes it unsuitable for SiC growth.” Wang, at p. 118.
The longstanding need for, and problem of obtaining high purity silicon carbide, and the failing of the art to provide a viable (both from a technical and economical standpoint) method of obtaining this material was also recognized in Zwieback et al., 2013/0309496 (“Zwieback”), which provides that the “[a]vailability of high-purity SiC source material is important for the growth of SiC single crystals in general, and it is critical for semi-insulating SiC crystals” (Zwieback at ¶0007). Zwieback goes on to state that the prior methods including liquid based methods have consistently failed to meet this need: “While numerous modifications of the Acheson process have been developed over the years, the produced SiC material always contain high concentrations of boron, nitrogen aluminum and other metals, and is unsuitable as a source material for the growth of semiconductor-quality SiC crystals” (Zwieback at ¶0009); “commercial grade bulk SiC produced by CVD is not pure enough for the use as a source in SiC crystal growth” (Zwieback at ¶0010); the liquid process “produced SiC material contains large concentrations of contaminates and is unsuitable for the growth of semiconductor-quality SiC crystals” (Zwieback at ¶0011); and, the direct synthesis of SiC provides an impure material that “precludes the use of such material” (Zwieback at ¶0015). Zwieback itself seeks to address this long-standing need with a complex, multi-step version of what appears to be the direct process in a stated attempt to provide high purity SiC. It is believed that this process is neither technically or economically viable; and therefor that it cannot solve the longstanding need to provide commercial levels of high purity SiC.
Thus, although there are other known methods of obtaining silicon carbide, it is believed that none of these methods provide the requisite technical, capacity, and economical viability to provide the purity levels, amounts, and low cost required for commercial utilization and applications; and in particular to meet the ever increasing demands for semiconductor grade material, and other developing commercial utilizations and applications. “Among these synthesis methods, only CVD has been successfully used to produce high purity SiC powder, it is not suitable for mass production because of high costs associated with CVD technology.” Wang, at p. 118.
CVD generally refers to Chemical Vapor Deposition. CVD is a type of vapor deposition technology. In addition to CVD, vapor deposition technologies would include PVD (Physcial Vapor Deposition), plasma enhanced CVD, Physical Vapor Transport (PVT) and others.
Thus, for these end products, and uses, among others that require high purity materials, there is an ever increasing need for low cost silicon carbide raw material that has a purity of at least about 99.9%, at least about 99.99%, at least about 99.999%, and least about 99.9999% and at least about 99.99999% or greater. However, it is believe that prior to embodiments of the present inventions, for all practical purposes, this need has gone unmet.
Further, prior to embodiments of the present inventions, it is believed that high purity and ultrahigh purity SiOC materials, and in particular in quantities larger than small laboratory batches of a few ounces, have never been obtained, and thus their importance, benefits, and the need for such material, has gone largely unrecognized and unappreciated.
High purity single crystalline silicon carbide material has many desirable features and characteristics. For example, it is very hard having a Young's modulus of about 424 GPa. Polycrystalline silicon carbide may also have very high hardness, depending upon its grain structure and other factors.
As used herein, unless specified otherwise, the terms specific gravity, which is also called apparent density, should given their broadest possible meanings, and generally mean weight per until volume of a structure, e.g., volumetric shape of material. This property would include internal porosity of a particle as part of its volume. It can be measured with a low viscosity fluid that wets the particle surface, among other techniques.
As used herein, unless specified otherwise, the terms actual density, which may also be called true density, should be given their broadest possible meanings, and general mean weight per unit volume of a material, when there are no voids present in that material. This measurement and property essentially eliminates any internal porosity from the material, e.g., it does not include any voids in the material.
Thus, a collection of porous foam balls (e.g., Nerf® balls) can be used to illustrate the relationship between the three density properties. The weight of the balls filling a container would be the bulk density for the balls:
      Bulk    ⁢                  ⁢    Density    =            weight      ⁢                          ⁢      of      ⁢                          ⁢      balls              volume      ⁢                          ⁢      of      ⁢                          ⁢      container      ⁢                          ⁢      filled      
The weight of a single ball per the ball's spherical volume would be its apparent density:
      Apparent    ⁢                  ⁢    Density    =            weight      ⁢                          ⁢      of      ⁢                          ⁢      one      ⁢                          ⁢      ball              volume      ⁢                          ⁢      of      ⁢                          ⁢      that      ⁢                          ⁢      ball      
The weight of the material making up the skeleton of the ball, i.e., the ball with all void volume removed, per the remaining volume of that material would be the actual density:
      Actual    ⁢                  ⁢    Density    =            weight      ⁢                          ⁢      of      ⁢                          ⁢      material              volume      ⁢                          ⁢      of      ⁢                          ⁢      void      ⁢                          ⁢      free      ⁢                          ⁢      material      
As used herein, unless stated otherwise, room temperature is 25° C. And, standard ambient temperature and pressure is 25° C. and 1 atmosphere.
Generally, the term “about” as used herein unless specified otherwise is meant to encompass a variance or range of ±10%, the experimental or instrument error associated with obtaining the stated value, and preferably the larger of these.